| Thanks for all of the helpful advice.
| I had actually given a quick try at this already with a spade bit and
| an anemic corded drill and was afraid that I wouldn't live long enough
| to finish all of the holes. I'll definitely buy an auger bit.
| I was already thinking about the electric shock hazard (esp. for the
| two poles which are not adjacent to the dock). The pneumatic drill
| sounds like a good idea, but I don't presently own one. Hey, perhaps
| this is a good excuse to buy another tool!! Is a high speed drill, or
| a low speed (higher torque) drill more appropriate for this task (I'm a
| novice at at this)?
| I already own an assortment of air wrenches (ratchet and impact); it
| seems a shame that I couldn't somehow easily adapt one of these.
You have had lots of advice, but, nobody has mentioned a "ship's auger". What you want to do is exactly why they were invented centuries ago. I have a 3/8" and 1/2" that I needed for just such a task.
They come in big bore sizes and all have up to a 3 foot shaft. You might be able to find one that is big enough and fits a 1/2" drill.